title: Low-density lipoprotein receptor related protein-1 (LRP1)-dependent cell signaling promotes neurotrophic activity in embryonic sensory neurons.
abstract: Developing sensory neurons require neurotrophic support for survival, neurite outgrowth and myelination. The low-density lipoprotein receptor-related protein-1 (LRP1) transactivates Trk receptors and thereby functions as a putative neurotrophin. Herein, we show that LRP1 is abundantly expressed in developing dorsal root ganglia (DRG) and that LRP1-dependent cell signaling supports survival, neurite extension and receptivity to Schwann cells even in the absence of neurotrophins. Cultured embryonic DRG neurons (E15) were treated with previously characterized LRP1 ligands, LRP1-receptor binding domain of α2-macroglobulin (RBD), hemopexin domain of MMP-9 (PEX) or controls (GST) for two weeks. These structurally diverse LRP1 ligands significantly activated and sustained extracellular signal-regulated kinases (ERK1/2) 5-fold (p<0.05), increased expression of growth-associated protein-43(GAP43) 15-fold (P<0.01), and increased neurite outgrowth 20-fold (P<0.01). Primary sensory neurons treated with LRP1 ligands survived > 2 weeks in vitro, to an extent equaling NGF, a finding associated with canonical signaling mechanisms and blockade of caspase-3 cleavage. LRP1 ligand-induced survival and sprouting were blocked by co-incubation with the LRP1 antagonist, receptor associated protein (RAP), whereas RAP had no effect on NGF-induced activity. Site directed mutagenesis of the LRP1 ligand, RBD, in which Lys(1370) and Lys(1374) are converted to alanine to preclude LRP1 binding, were ineffective in promoting cell signaling, survival or inducing neurite extension in primary sensory neurons, confirming LRP1 specificity. Furthermore, LRP1-induced neurite sprouting was mediated by Src-family kinase (SFK) activation, suggesting transactivation of Trk receptors. Co-cultures of primary embryonic neurons and Schwann cells showed that LRP1 agonists promoted axonal receptivity to myelination to Schwann cells. Collectively, these findings identify LRP1 as a novel and perhaps essential trophic molecule for sensory neuronal survival and development.
authors.affiliation: Department of Anesthesiology, School of Medicine, University of California San Diego, La Jolla, California, United States of America ; Department of Orthopedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Kazuyo
authors.initials: K
authors.lastname: Yamauchi
authors.forename: Tomonori
authors.initials: T
authors.lastname: Yamauchi
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Mantuano
authors.forename: Kenichi
authors.initials: K
authors.lastname: Murakami
authors.forename: Kenneth
authors.initials: K
authors.lastname: Henry
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Takahashi
authors.forename: Wendy Marie
authors.initials: WM
authors.lastname: Campana
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D019922:GAP-43 Protein / Q000378:metabolism; D005727:Ganglia, Spinal / Q000378:metabolism; D008024:Ligands; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000502:physiology; D009414:Nerve Growth Factors / Q000378:metabolism; D016501:Neurites / Q000378:metabolism; D027361:Organic Anion Transporters / Q000378:metabolism; D016716:PC12 Cells; D053402:PHEX Phosphate Regulating Neutral Endopeptidase / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D020917:Receptor, trkA / Q000378:metabolism; D012583:Schwann Cells; D011984:Sensory Receptor Cells / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D000511:alpha-Macroglobulins / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D019922:GAP-43 Protein; D008024:Ligands; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D009414:Nerve Growth Factors; D027361:Organic Anion Transporters; D000511:alpha-Macroglobulins; D020917:Receptor, trkA; D019061:src-Family Kinases; D053402:PHEX Phosphate Regulating Neutral Endopeptidase; C506229:Phex protein, rat